The present invention relates to a new and improved method of configuring, shaping or forming the tooth bearing pattern or localized tooth contact of gears containing teeth of a cycloidally arcuate shape as well as a face cutter head for performing the method.
With respect to the method of the present development, such in its more particular aspects is of the type comprising the steps of cutting tooth gaps or spaces by using a rotating face cutter head or face-mill gear cutter having a rotational axis about which the face cutter head rotates, and provided with cutters or cutter blades which have inner and outer cutting edges for machining the outer and inner tooth flanks of the gear teeth.
With respect to the apparatus of the present development, such in its more particular aspects concerns an improved face cutter head or face-mill gear cutter useful for carrying out the method as mentioned hereinbefore.
A method of and a cutter head pair for lengthwise crowning of the longitudinally curved gear teeth of a pair of bevel gears or hypoid gears is known, for example, from Swiss Pat. No. 417,284. The crowning of the teeth is achieved by inclining the cutter head rotational axis in a radial plane extending through a selected computation point of a tooth flank. Since the cutter head rotational axis no longer extends perpendicularly with respect to the crown gear plane, the end regions of the tooth gaps or spaces are cut somewhat deeper into the gear blank. However, since the cutting edges of the cutters in the cutter head are inclined at a pressure angle with respect to a line extending perpendicular to the plane of the crown gear, the longitudinal lines of the gear teeth will deviate from the cycloid shape at the end regions of the tooth gaps or spaces. When two tooth flanks thus produced mesh, they only will contact at the central region of the teeth.
In practical operation during which the teeth are loaded and have to transfer torque or rotational moment, the conditions at the region of contact between two corresponding tooth flanks will change. This is so because the shafts upon which the gears are mounted and the housing at which the shafts are journalled deform under the load to be transferred. Additionally, the teeth of the gears, also, will deform under load. It will thus be readily seen that the conditions of contact between two tooth flanks or the tooth bearing pattern or localized tooth contact may appreciably change under load.
Using the known method the tooth bearing pattern may be kept under control by suitable choice of the crowning as long as the orientation angle of the cutters, i.e. the angle through which the cutters are rotated with respect to a corresponding cutter radius, assume modest values.
The selection of larger orientation angles is limited in the prior art method by the change in the tooth bearing thus effected.